Sign up to receive free email alerts when patent applications with chosen keywords are publishedSIGN UP

Abstract:

The invention provides for a cermet powder containing 75-90% by weight
of at least one hard material powder, from 10 to 25% by weight of one or
more matrix metal powders and up to 3% by weight of at least one
modifier,wherein the matrix metal powder or powders contain from 0 to 38%
by weight of cobalt, from 0 to 38% by weight of nickel, from 0 to 20% by
weight of aluminum, from 0 to 90% by weight of iron and from 10 to 35% by
weight of chromium andthe sum of the contents of iron and chromium is in
the range from 10 to 95% by weight and the sum of the contents of cobalt,
nickel and iron is in the range from 65 to 95% by weight. The invention
also relates to a cermet and a process to make the cermet containing the
cermet powder and shaped article coated with the cermet powder and a
process to make the shaped article.

Claims:

1-18. (canceled)

19. A cermet powder comprising75-90% by weight of at least one hard
material powder,from 10 to 25% by weight of one or more matrix metal
powders andup to 3% by weight of at least one modifier,wherein the matrix
metal powder or powders containfrom 0 to 38% by weight of cobalt,from 0
to 38% by weight of nickel,from 0 to 20% by weight of aluminum,from 0 to
90% by weight of iron andfrom 10 to 35% by weight of chromium andthe sum
of the contents of iron and chromium is in the range from 10 to 95% by
weight and the sum of the contents of cobalt, nickel and iron is in the
range from 65 to 95% by weight.

20. The cermet powder as claimed in claim 19, which comprisesfrom 75-90%
by weight of at least one hard material powder,from 10 to 25% by weight
of one or more matrix metal powders andup to 3% by weight of
modifiers,wherein the matrix metal powder or powders containfrom 0 to 38%
by weight of cobalt,from 0 to 38% by weight of nickel,from 0 to 20% by
weight of aluminum,from 0 to 75% by weight of iron andfrom 20 to 35% by
weight of chromium andthe sum of the contents of iron and chromium is in
the range from 25 to 95% by weight and the sum of the contents of cobalt,
nickel and iron is in the range from 65 to 75% by weight.

21. The cermet powder as claimed in claim 19, wherein the matrix metal
powder contains from 0 to 75% by weight of iron.

22. The cermet powder as claimed in claims 19, wherein the sum of the
contents of cobalt, nickel and iron is in the range from 65 to 75% by
weight.

23. The cermet powder as claimed in claim 19, wherein the nickel and
cobalt are present in the matrix powder or powders in a weight ratio of
at least 2:3.

24. The cermet powder as claimed in claim 19, wherein the matrix powder or
powders are cobalt-free.

25. The cermet powder as claimed in claim 19, wherein the matrix powder or
powders are cobalt- and nickel-free.

26. The cermet powder as claimed in claim 19, wherein the content of iron
in the matrix powder or powders is at least 30% by weight.

27. The cermet powder as claimed in claim 19, wherein the sum of the
contents of iron and chromium of the matrix powder or powders is at least
60% by weight.

28. The cermet powder as claimed in claim 19, wherein the ratio of the sum
of the contents of chromium and aluminum to the sum of the contents of
iron, nickel and chromium in parts by weight is from 1:2.2 to 1:3.7.

29. The cermet powder as claimed in claim 19, wherein the matrix powder
has the composition: from 20 to 26% by weight of chromium, from 64 to 72%
by weight of iron and from 5 to 16% by weight of aluminum.

30. The cermet powder as claimed in claim 19, wherein the hard material
powder is a powder selected from the group consisting of WC,
Cr3C2, VC, TiC, B4C, TiCN, SiC, TaC, NbC, Mo2C and
mixtures thereof.

31. The cermet powder as claimed in claim 19, wherein the modifier is
selected from the group consisting of Mo, Nb, Si, W, Ta, V and mixtures
thereof.

32. A process for coating a surface with comprises thermal spray coating
the surface with the powder as claimed in claim 19.

33. A cermet having the composition as claimed in claim 19.

34. A shaped article which has a coating comprising the cermet as claimed
in claim 33.

35. A process for producing the cermet as claimed in claim 33 which
comprisesproviding a powder in a form or preparation which is suitable
for thermal spraying;carrying out a thermal spraying process using this
powder;obtaining the cermet andwherein the powder comprises75-90% by
weight of at least one hard material powder,from 10 to 25% by weight of
one or more matrix metal powders andup to 3% by weight of at least one
modifier,wherein the matrix metal powder or powders containfrom 0 to 38%
by weight of cobalt,from 0 to 38% by weight of nickel,from 0 to 20% by
weight of aluminum,from 0 to 90% by weight of iron andfrom 10 to 35% by
weight of chromium andthe sum of the contents of iron and chromium is in
the range from 10 to 95% by weight and the sum of the contents of cobalt,
nickel and iron is in the range from 65 to 95% by weight.

36. A process for producing the shaped article as claimed in claim 34
which comprisesproviding a powder in a form or preparation which is
suitable for thermal spraying;carrying out a thermal spraying process
using this powder;obtaining the article andwherein the powder
comprises75-90% by weight of at least one hard material powder,from 10 to
25% by weight of one or more matrix metal powders andup to 3% by weight
of at least one modifier,wherein the matrix metal powder or powders
containfrom 0 to 38% by weight of cobalt,from 0 to 38% by weight of
nickel,from 0 to 20% by weight of aluminum,from 0 to 90% by weight of
iron andfrom 10 to 35% by weight of chromium andthe sum of the contents
of iron and chromium is in the range from 10 to 95% by weight and the sum
of the contents of cobalt, nickel and iron is in the range from 65 to 95%
by weight.

37. A process for producing the cermet as claimed in claim 33, which
comprisesproviding a powder;shaping the powder under pressure to give a
green body;heating the green body to give the cermet andwherein the
powder comprises75-90% by weight of at least one hard material
powder,from 10 to 25% by weight of one or more matrix metal powders andup
to 3% by weight of at least one modifier,wherein the matrix metal powder
or powders containfrom 0 to 38% by weight of cobalt,from 0 to 38% by
weight of nickel,from 0 to 20% by weight of aluminum,from 0 to 90% by
weight of iron andfrom 10 to 35% by weight of chromium andthe sum of the
contents of iron and chromium is in the range from 10 to 95% by weight
and the sum of the contents of cobalt, nickel and iron is in the range
from 65 to 95% by weight.

38. A process for producing the article as claimed in claim 34, which
comprises the steps:providing a powder;shaping the powder under pressure
to give a green body;heating the green body to give the article
andwherein the powder comprises75-90% by weight of at least one hard
material powder,from 10 to 25% by weight of one or more matrix metal
powders andup to 3% by weight of at least one modifier,wherein the matrix
metal powder or powders containfrom 0 to 38% by weight of cobalt,from 0
to 38% by weight of nickel,from 0 to 20% by weight of aluminum,from 0 to
90% by weight of iron andfrom 10 to 35% by weight of chromium andthe sum
of the contents of iron and chromium is in the range from 10 to 95% by
weight and the sum of the contents of cobalt, nickel and iron is in the
range from 65 to 95% by weight. 671774 1 10

[0002]Such powders comprise at least one finely divided hard material
powder such as WC, Cr3C2, TiC, B4C, TiCN, Mo2C, etc.,
and a finely divided metal or alloy matrix powder. Hard material powder
and matrix powder are intensively mixed, usually in the presence of a
solution of an organic binder, if appropriate with comilling, atomized,
dried, sieved and subsequently heated under a hydrogen-containing
atmosphere to remove the organic binder and produce a sintered bond so
that relatively large agglomerates having a particle size of from 10 to
100 μm are formed.

[0003]DE-B2-1446207 discloses a flame spraying powder which contains metal
carbides as hard material and from 10 to 45% of aluminum and nickel as
metal.

[0004]As matrix metal powders, cobalt- and nickel-containing powders, in
particular, have become established in the industry.

[0005]It is a first object of the invention to reduce the use of cobalt
further since cobalt has become a raw material for which demand exceeds
supply because of its widespread use.

[0006]A further object of the invention is to provide low-cobalt cermet
coatings which compared to customary Co--Cr matrix alloys have comparable
or increased abrasion resistance and cavitation resistance.

[0007]Another object of the invention is to increase the corrosion
resistance of cermet coatings, in particular to reduce the solubility of
matrix metals from the coatings.

[0008]The invention provides cermet powders containing 75-90% by weight of
at least one hard material powder and from 10 to 25% by weight of one or
more matrix metal powders and also up to 3% by weight of modifiers,

[0009]wherein the matrix metal powder or powders contain [0010]from 0 to
38% by weight of cobalt, [0011]from 0 to 38% by weight of nickel,
[0012]from 0 to 20% by weight of aluminum, [0013]from 0 to 90% by weight
of iron and [0014]from 10 to 35% by weight of chromium and [0015]the sum
of the contents of iron and chromium is in the range from 10 to 95% by
weight and the sum of the contents of cobalt, nickel and iron is in the
range from 65 to 95% by weight.

[0016]Advantageous cermet powders are powders which contain 75-90% by
weight of at least one hard material powder and from 10 to 25% by weight
of one or more matrix metal powders and also up to 3% by weight of
modifiers, wherein the matrix metal powder or powders contain up to 38%
by weight of cobalt, up to 38% by weight of nickel, up to 20% by weight
of aluminum, up to 90% by weight, advantageously up to 75% by weight, of
iron and from 20 to 35% by weight of chromium and the sum of the contents
of iron and chromium is in the range from 25 to 95% by weight and the sum
of the contents of cobalt, nickel and iron is in the range from 65 to 95%
by weight, advantageously from 65 to 75% by weight.

[0017]Particularly advantageous cermet powders are powders as claimed in
claim 1 containing 75-90% by weight of at least one hard material powder
and from 10 to 25% by weight of one or more matrix metal powders and also
up to 3% by weight of modifiers, wherein the matrix metal powder or
powders contain [0018]from 0 to 38% by weight of cobalt, [0019]from 0
to 38% by weight of nickel, [0020]from 0 to 20% by weight of aluminum,
[0021]from 0 to 75% by weight of iron and [0022]from 20 to 35% by weight
of chromium and

[0023]the sum of the contents of iron and chromium is in the range from 25
to 95% by weight and the sum of the contents of cobalt, nickel and iron
is in the range from 65 to 75% by weight.

[0024]A further embodiment of the invention provides cermet powders
containing 75-90% by weight of at least one hard material powder and from
10 to 25% by weight of one or more matrix metal powders and also up to 3%
by weight of modifiers,

[0025]wherein the matrix metal powder or powders contain [0026]from 0 to
38% by weight of cobalt, [0027]from 0 to 38% by weight of nickel,
[0028]from 0 to 20% by weight of aluminum, [0029]from 30 to 90% by weight
of iron, advantageously [0030]from 30 to 75% by weight of iron, and
[0031]from 10 to 35% by weight of chromium and

[0032]the sum of the contents of iron and chromium is in the range from 10
to 95% by weight, advantageously from 60 to 95% by weight, and the sum of
the contents of cobalt, nickel and iron is in the range from 65 to 95% by
weight.

[0033]In preferred cermet powders according to the invention, the matrix
metals nickel and cobalt are present in a weight ratio of at least 2:3,
more preferably in a weight ratio of 1:1, particularly preferably in a
weight ratio of 3:2.

[0034]Particularly preferred cermet powders according to the invention are
cobalt-free. Further preferred cermet powders are cobalt- and
nickel-free.

[0035]More preferred, in particular low-cobalt or cobalt-free, cermet
powders according to the invention have a content of iron in the matrix
metal of at least 30% by weight, with the sum of the contents of iron and
chromium in the matrix powder or powders being at least 60% by weight. In
such cermet powders, the matrix metal powder or powders contain
[0036]from 0 to 10% by weight of cobalt, [0037]from 0 to 38% by weight of
nickel, [0038]from 0 to 20% by weight of aluminum, [0039]from 30 to 90%
by weight of iron, advantageously [0040]from 30 to 75% by weight of iron,
and [0041]from 10 to 35% by weight of chromium.

[0042]In cermet powders of the invention, in particular cobalt-free cermet
powders of the invention, the ratio of the sum of the contents of
chromium and aluminum to the sum of the contents of iron, nickel and
chromium in parts by weight is preferably from 1:2.2 to 1:3.7,
particularly preferably from 1:2.7 to 1:3.6.

[0043]A preferred composition can have from 20 to 26% by weight of
chromium, from 64 to 72% by weight of iron and from 5 to 16% by weight of
aluminum.

[0045]The matrix powders can be produced in a manner known per se by
atomization of metal or alloy or part alloy melts. When part alloy
powders or metal powders which have not been prealloyed are used,
alloying occurs during use (for example during spray application) of the
cermet powders.

[0046]Preferred cobalt, nickel and/or iron part alloy matrix powders are
obtained by chemical precipitation by reaction of appropriate salts with
excess oxalic acid, drying and thermal treatment as described in DE 198
22 663 A1 or U.S. Pat. No. 6,554,885 B1, with chromium being mixed in as
metal powder.

[0049]The present invention also provides a cermet which has the
above-described composition and also a shaped article coated with such a
cermet.

[0050]To produce these cermet powders, the hard material powder or powders
and the matrix powder or powders and also modifiers having, if
appropriate, different average particle sizes which should, however, in
each case be less than 10 μm in diameter are slurried in a manner
known per se in an aqueous solution of an organic binder and homogenized
by means of mix-milling in a ball mill, an attritor or a stirred vessel
and the suspension is atomized in a spray dryer, with the water
evaporating from the sprayed droplets. The resulting powder agglomerate
is converted into a powder having an intended particle size by means of
classification processes (sieving, sifting) and the organic binder of the
agglomerate is released into a hydrogen-containing atmosphere by
sintering at a temperature of up to about 1300° C., in particular
from 1100° C. to 1300° C. The resulting sinter cake is
converted back into powder having the intended particle size range by
physical treatment (crushing, milling, sieving, sifting).

[0051]A cermet according to the invention can be obtained by pressing and
sintering of the cermet powders described or else by thermal spraying,
i.e. by means of a thermal spraying process such as high-velocity flame
spraying, cold gas spraying, plasma spraying or similar processes. The
present invention therefore likewise provides a process for producing a
cermet or an article having the above-described composition, which
comprises the steps: [0052]providing a powder as claimed in one or more
of claims 1 to 11 in a form or preparation which is suitable for thermal
spraying; [0053]carrying out a thermal spraying process using this
powder; [0054]obtaining the cermet or the article.

[0055]The present invention therefore likewise provides a process for
producing a cermet or an article having the above-described composition,
which comprises the steps: [0056]providing a powder as claimed in one
or more of claims 1 to 11; [0057]shaping the powder under pressure to
give a green body; [0058]heating the green body to give the cermet or the
article.

EXAMPLES 1 TO 7

[0059]A tungsten carbide powder having a particle size of 0.9 μm
determined by FSSS, a carbon content of 6.1% by weight and a content of
free carbon of 0.05% by weight was used in each case.

[0060]The matrix powder 1 (table 1) of examples 1 to 5 having the
composition indicated there was produced by chemical precipitation using
a method analogous to example 2 of DE 198 22 663 A1. The particle size
was 1.4-2.2 μm FSSS at a specific surface area determined by the BET
method of 1.8-2.6 m2/g. The matrix powder 2 of examples 1 to 3 is an
electrolytically produced powder having a particle size D50 of 3.1 μm
(laser light scattering).

[0061]The matrix metal powder of examples 6 and 7 was obtained by
atomization of an alloy melt of Fe, Cr and Al. The particle size D90 was
10.8 and 10.2 μm, respectively (laser light scattering).

[0062]About 50 kg of cermet powder composed of WC and matrix alloys of the
composition shown in table 1 were introduced into an initial charge of 10
l of water containing about 1% of polyvinyl alcohol (PVA, Shin-Etsu,
GP05) as binder and about 0.5% of Nalco (Deutsche Nalco GmbH) as wetting
agent and homogenized by means of a ball mill, the homogenized suspension
was atomized in a commercial spray dryer and the water was evaporated
from the spray droplets. The agglomerated powder obtained in this way is
subjected to a thermal treatment and the bond is thereby converted into a
sintered bond. The sintered cake obtained in this way is converted into
powder in the intended particle size range by crushing, milling, sieving
and sifting. The carbon content, the average particle size determined by
laser light scattering, the particle size distribution and the bulk
density of the cermet powders are reported in table 1.

[0063]Coatings on building steel ST37 were produced from the powders by
means of high-velocity flame spraying (HVOF system Diamond Jet Hydrid
2600).

[0064]Table 2 reports the properties of the coatings.

[0065]FIG. 1 shows optical micrographs of the microstructure of the
coatings produced using the powders from examples 1 (FIG. 1a)), 2 (FIG.
1b)) and 3 (FIG. 1c)). FIG. 2 shows optical micrographs of the
microstructure of the coatings produced using the powder from example 7
and using the spray parameters "standard" (FIG. 2a)), "cold and fast"
(FIG. 2b)) and "hot and slow" (FIG. 2c)), respectively.